Various reinforcements are commonly implemented in a vehicle body in order to increase the rigidity of a floor panel and other flat panels, as disclosed in Japanese Patent Application Laid-Open Publication No. 07-291150 (JP 07-291150 A).
In the vehicle body structure disclosed in JP 07-291150 A, a bead (longitudinal bead) that is long and thin in the longitudinal direction of the vehicle body and a bead (transverse bead) that is long and thin in the width direction of the vehicle are formed so as to intersect with each other on the top surface of the floor panel, and a cross member that is long and thin in the width direction of the vehicle is laid over and bonded to the top of the transverse bead, thereby increasing the rigidity of the floor panel.
However, in the aforementioned vehicle body structure, the portion where the longitudinal bead and the transverse bead (equivalent to the floor frame) intersect is no more than a mere space. Specifically, the distal end of the longitudinal bead passes through the vertical walls of the transverse bead. Thus, there is room for improvement in increasing the rigidity of the floor panel in the portions where the beads intersect with each other (particularly, the rigidity with respect to loads acting in the vertical direction of the vehicle body), by means of the longitudinal bead and the transverse bead.
Furthermore, in the aforementioned vehicle body structure, a cross member that is long and thin in the width direction of the vehicle is laid over the transverse bead and is bonded to the longitudinal bead. However, there is a limit on how much of an increase can be achieved by means of this type of configuration in the rigidity of the floor panel in the portions where the beads intersect with each other (particularly, the rigidity with respect to loads acting in the vertical direction of the vehicle body).
Because of this, consideration has been given to adding separate members to increase the rigidity of the intersecting portions, but merely adding members would lead to an increase in the weight of the vehicle body.